HAT-P-28

HAT-P-28 is the primary of a binary star system about 1320 light-years away. It is a G-type main-sequence star. The star's age is older than the Sun's at 6.1^+2.6
_−1.9 billion years.^[3] HAT-P-28 is slightly enriched in heavy elements, having a 130% concentration of iron compared to the Sun. Evolutionary modelling shows it to be right at the end of its main sequence life.^[2] The binary star system is suspected to be surrounded by a debris disk with a 6.1″(2500 AU) radius.^[7]

HAT-P-28

Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda[1]
Right ascension	00h 52m 00.1876s[2]
Declination	+34° 43′ 42.205″[2]
Apparent magnitude (V)	13.03[3]
Characteristics
Evolutionary stage	main sequence[3]
Spectral type	G3[3]
Astrometry
Radial velocity (Rv)	48.06[4] km/s
Proper motion (μ)	RA: 25.615(14) mas/yr[2] Dec.: 2.712(11) mas/yr[2]
Parallax (π)	2.4728±0.0156 mas[2]
Distance	1,319 ± 8 ly (404 ± 3 pc)
Orbit[5]
Primary	HAT-P-28
Companion	HAT-P-28 B
Semi-major axis (a)	0.994±0.002" (404 AU)
Details[6]
Mass	1.02±0.05 M☉
Radius	1.10+0.09 −0.07 R☉
Luminosity	1.13+0.23 −0.16[3] L☉
Surface gravity (log g)	4.36±0.06[3] cgs
Temperature	5680±90[3] K
Metallicity [Fe/H]	0.12±0.08[3] dex
Rotational velocity (v sin i)	0.2+0.5 −0.2[3] km/s
Age	6.1+2.6 −1.9[3] Gyr
Other designations
Gaia DR2 363702817083391232, GSC 02284-00503, 2MASS J00520018+3443422[4]
Database references
SIMBAD	data

The red dwarf stellar companion was detected in 2015 at a projected separation of 0.972″^[8] and confirmed in 2016 to be either bound or co-moving.^[5]

Planetary system

In 2011 a transiting hot Jupiter planet b was detected on a nearly circular orbit. The planetary equilibrium temperature is 1,384±52 K.^[3] No orbital decay was detected as in 2018, despite the close proximity of the planet to the host star.^[6]

The HAT-P-28 planetary system^[6][3]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.626±0.037 MJ	0.0434±0.0007	3.257215±0.000007	0.051±0.033	88.0±0.9°	1.190+0.102 −0.075 RJ